Kill Or Be Killed
by FangirlTrash
Summary: Frisk, accompanied by their companion Flowey, journeys through the Underground on a quest to escape through the barrier and get back to the surface. However, they will soon learn the hardships and struggles that they must face in order to achieve their goal. Underfell AU. Contains generally dark themes.
1. Chapter 1 - An Adventure Arises

**A/N: So, hello everyone. uwu I am happy to present my second fanfiction on this site, an Undertale one. Yeah, I'm kind of obsessed with Undertale now, whoops. ._. But I'll still continue MIBTF! I promise. I'll post the next chapter of that soon. But anyway, besides that, this is a fanfic on an AU I've fallen in love with of Undertale, called Underfell. Basically, it's a super edgy AU where everyone is evil except for Flowey, Frisk, and Chara. And I thought it would be fun to make a fanfiction out of it, lel. Most of the ideas for this are from Tumblr user hotlegmeme(NSFW blog, beware). I'm excited to see how this fanfic turns out, so, without further ado, let the first chapter begin!**

* * *

Long ago, two races ruled over Earth: humans and monsters. Humans feared the monsters, as they would often hide in the shadows and kill any human that they came in contact with. One day, war broke out between the two races. After a long battle, the humans were victorious. They sealed the monsters underground with a magic spell. Thus, the monsters grew disgusted with humans, and many swore to never forgive them for sealing them underground.

However, the barrier keeping the monsters trapped could be shattered with the power of seven human souls. The king of the monsters, King Asgore Dreemurr, swore to destroy every human who ever fell into the underground. If he ended up collecting seven souls, the entire race of monsters would be free once again.

But that hasn't happened yet. And it never will.

* * *

After being unconscious for who-knows-how-long, Frisk slowly opened their eyes to nothing but blatant darkness. They blinked, raising their head from the soft, comfortable ground beneath them. They tried to use their arm to prop up, but a shock of agony quickly raced through them, and a slight moan of pain escaped their lips as they lifted their arm back up.

Frisk bit their lip, silently hoping that their arm wasn't broken as they instead used their legs to get up. With their eyesight now adjusted to the dark, the small child looked around the room they were in. The walls were made of stone, and there was a small amount of sunlight filtering down where they stood. That must have been where they fell.

Frisk suddenly noticed a tunnel, or rather a hallway in front of them. _I don't have anywhere else to go,_ they thought solemnly to themself, slowly walking off the bed of golden flowers that they were previously lying on, and continued through the silent hallway.

After a short walk, they were welcomed by another small room. Though this time, there was a small grass patch in the middle. On the grass patch was a peculiar flower. The flower looked at Frisk and grinned—yes, grinned—and its gaze immediately brightened. Frisk walked up to it, rubbing the upper part of their arm awkwardly.

"Howdy!" the flower said gleefully, "I'm Flowey! Flowey the Flower! Hmmm…you're new to the underground, aren'tcha?"

Frisk nodded. They could hardly believe that a flower was having a conversation with them.

"Golly," Flowey exclaimed, "you must be so confused. Someone ought to teach you how things work around here! I guess little old me will have to do. Ready? Here we go!"

Frisk was about to ask what he meant by that, but they were quickly cut off. They gasped as they suddenly saw a red heart floating in front of them, just in between them and Flowey.

"See that heart?" Flowey explained. "That is your soul, the very culmination of your being! Your soul starts off weak, but can grow strong if you gain a lot of LV.

"What's LV stand for?" Frisk asked. They were still pretty stunned that their own soul was right in front of their very eyes.

"Why, LOVE of course!" Flowey suddenly looked like he was uneasy. "Uh…LOVE, too, is an acronym. It stands for "Level of Violence," a way of measuring someone's capacity to hurt. And if you kill a lot, you gain more LOVE."

Frisk's eyes widened. "Why would anyone ever want to kill?!" they asked.

"Oh, you'd be surprised…" Flowey's voice trailed off. He gazed down at the ground. "Monsters down here aren't exactly friendly. You're a human, right? Well, I'm sorry to tell you this, but you're in danger. Monsters kind of…loathe humans. Down here, its kill or be killed." The flower shuddered. "But…I'm scarred. _Terrified_ , actually. I'm just a small, defenseless flower. I hide here in the Ruins because most monsters don't normally come around these parts. But, I don't know how much more of this I can take!"

Frisk couldn't help but feel bad for him. "That's horrible," they murmured, sighing. What an awful world.

"If you're a human, then you probably came from the surface, right?"

Frisk nodded again. They had just noticed that their soul had disappeared from in front of them.

"Well, I'm sorry to say, but the only way back to where you came from is through the king's castle. That's where the barrier is located, which is where you can escape this wretched place. King Asgore, well…he's kinda a human-killing fanatic, so if you wanna get out of here, it'll be pretty hard to survive."

"Well," Frisk muttered, "um, why don't you come with me? If you live here, then you probably know your way around, and I'll need someone to help me. If you want, that is." They tried to sound strong and determined, but inside, their heart was racing. Could they really survive this type of kill-or-be-killed world? They didn't want to hurt anybody. They didn't even think that they could. They had never seen a real monster before, but they guessed that monsters were probably ten times stronger than humans were.

Flowey's smile returned to his face. "Come with you…?" he repeated. "You'd let me join you?"

"Of course!" Frisk said with false joy.

Flowey paused for a moment, pondering, then looked up sternly at Frisk to confirm. "Okay! I'll come! To be honest with you, it's actually a relief that you're letting me come with you. I'm so scared on my own…at least I'll have someone to protect me."

 _I'm not even sure if I'll be able to protect myself,_ Frisk said to themself, then shook off the thought. "So, how exactly are you planning on coming?" they asked Flowey. "You're kind of rooted to the ground."

"Oh, that's easy! Just pull me out."

Frisk raised an eyebrow.

"No, I'm serious. Pull me out. Really. I'm a monster, not some normal flower or anything; I won't die."

"Okay, okay, I got it," Frisk said, getting on one knee to crouch down. They reached out their hand and grabbed a hold of Flowey's stem. Suddenly, they winced and drew their arm back. "I forgot," they sighed, "I think my arm is broken from the fall."

"Hmm," Flowey thought for a moment. "Not to worry! I've got an idea. First, pull me out."

Frisk grabbed Flowey again, this time with their good arm, and yanked them out of the ground. It was surprisingly easy, but that was probably due to the fact that it appeared that Flowey didn't have any roots, only a rather long stem.

"Okay," Flowey instructed," now place me on your broken arm…carefully, so that you don't hurt yourself too bad. Just trust me on this."

Frisk, although unsure, did as told and stretched out their arm, placing Flowey on top of it. With this, Flowey stretched out his stem, wrapping it around Frisk's entire limb. Frisk felt themself loose most of their feeling in their arm, yet it was pretty relieving.

"So I have control of your arm now…at least, I think that's how it works," Flowey said. "But don't worry! It's not like I'll move it or anything. I'll try to stay as still as I can be; I don't want to make it worse than it already is."

"Okay," Frisk said, smiling at the small flower. "I trust you."

"Thanks, um…hey, I realized I never asked you this, but…what's your name?"

"My name? It's Frisk."

"Oh, well…thank you, Frisk." Frisk had never seen a flower blush before. Flowey continued, "I hope we can be good friends. Anyway, if we wanna get out of here, we'll have to escape the Ruins first, and that'll be hard, considering the fact that a certain monster lives here. She may look soft and kind on the outside, but trust me, she won't hesitate to eat you."

Frisk blinked, and Flowey smirked. "Yeah, I didn't stutter. Eat you. It's kinda her thing. Weird, huh? But, hey, I'm not judging or anything. So…maybe we can get by without meeting her. Either way, we better get going. So, onwards, Frisk!"

Frisk chuckled with amusement. They walked forward, towards what seemed to be the exit of the room, which only led to another room. But Flowey seemed to know how to navigate this place, so with the small flower as their companion, they hoped that they could accomplish their goal—to escape the underground and get home safely. Which, seemed sort of impossible, from how gruesome this place was made out to be…but with enough determination, they could accomplish anything! Or, they could try to, anyway.

Frisk looked back at Flowey resting on their arm as they walked. He was staring out in front of them, smiling, his eyes shining with hope.

This was the beginning of a grand adventure.

* * *

 **A/N: Sorry if that ending was painfully cheesy lmao. I tried. Also, I almost forgot to mention that this will most likely be a neutral run of Undertale, or rather, Underfell. So some characters will die, while others won't. I'm going to refrain from making this a true pacifist, for the sake of the super edgy and angsty AU that this is. After all, it's kill or be killed. C: BUT. In some alternate timeline, if I** _ **ever**_ **end up finishing this fanfiction, then I'll probably consider writing another that is a true pacifist run of Underfell. So, who knows? Anyway, that's it. Nyeh heh heh. /rolls away**


	2. Chapter 2 - What a Dummy!

**A/N: ugh i'm sorry this took so long wow…heh anyway, here's chapter two~**

* * *

"Woah, what's that?!"

Frisk eagerly ran through the small room, stopping in front of a strange sparkling shape. Their eyes glistened as they gazed at it.

Flowey smirked. "You're too easily distracted," he chuckled. "That's called a SAVE Point. With it, you can SAVE your game."

"My…game?" Frisk looked at Flowey with a confused expression.

"Well, you'll probably see what I mean later on," Flowey explained. "You possess some strange and unique powers, Frisk. Whenever you see one of those sparkles, it's pretty important to SAVE. So, go ahead. Uh…poke it or something."

Frisk nodded, even though they were still confused. They did as they were told, reaching out their hand and poking the SAVE Point quickly.

 _The shadow of the ruins looms above, filling you with determination._

"Hey, you did it," Flowey said, clearly pleased. "Now, let's keep heading forward.

Yet he was often annoyed with how distracted Frisk was, always having to inspect and take a look at every single object they passed by, Flowey had to admit that he enjoyed the kid's company. He had felt so alone ever since…well, no need to dwell on the past.

Flowey was also glad to know that Frisk was a quick learner. They completed puzzles with ease after Flowey gave them a simple explanation on how it worked. Maybe they could actually make it out of the Ruins alive.

* * *

It wasn't long until they came across a room with a single dummy.

"I don't remember that being there before," Flowey commented, eyeing the dummy suspiciously. Something about it was off. "We should probably steer clear of—h-hey, Frisk! Stop!"

Before he knew it, Frisk was hurriedly walking towards the dummy with interest. Was the kid even listening to him? "Frisk, I'm serious," Flowey warned. "That dummy might be—"

But of course, it was too late. Frisk screamed and backed away as the dummy suddenly flew up into the air, its mouth curling into a menacing sneer. It spoke, "FOOL! Does a human like _you_ really think you can approach _me_?! Ha!"

It took one glance at Frisk's face(who was on the verge of tears), and Flowey was immediately filled with hate for the dummy. "Get away from them!" Flowey shouted, which only made the dummy laugh.

"FOOLS! Do you know who I am?! I am a ghost that lives inside a dummy! My cousin lives inside a dummy too, and they told me that if I ever see a human, then I should eliminate them immediately! That being said…DIE!"

Frisk was going to panic. Their surroundings suddenly vanished, replaced with a black void of nothingness. And, just like when they met Flowey, their soul floated in front of them. But this time, something was different. Before them appeared four options. FIGHT, ACT, ITEM, and MERCY. Frisk looked back up at the dummy, who was now more intimidating than ever.

 _Dummy attacks!_

Frisk looked at Flowey for guidance. "What do I do?!" they cried, wiping some tears away with their sleeve using a wobbly, shaking arm. "I'm scared!"

Flowey tightened his stem's grip on Frisk's arm to make sure that he wouldn't fall off or anything during the fight. Because…by the look of things, this was going to be one tough fight. He glanced at Frisk and returned their gaze with a reassuring smile, even though he was probably as scarred as the kid was. Years and years of dying will do that to you. Now that he thought about it…what would happen if _Frisk_ died? Surely they would reset, but would he even remember anything that happened? Frisk's determination was much greater than his, so…

"Flowey!"

Flowey hissed. This was no time to be thinking. He had to stay focused, for Frisk's sake.

"Alright, listen," Flowey explained to them as calmly as he could, "do you see those, er, options in front of you? Yea, well, when you're in a fight, those'll always pop up. What you can do is move your soul to the option that you want. The names are pretty self-explanatory, so I won't talk about that right now; I'm sure you can figure that out for yourself. What I recommend doing is—"

Before he could finish, Frisk had already selected the ACT option. More options appeared before them, but before they could read it, Flowey spat, "What are you doing?! Don't ACT! It'll get you killed! If you want to survive long enough to get out of the Underground, let alone the Ruins, you have to learn to fight back!"

"But I don't want to fight!" Frisk protested.

Flowey rolled his eyes. "Look, Frisk, you're a smart kid, but wits won't always help you, especially against a monster like this. Now, please, listen to me, for your own good. Select the FIGHT option, then hit the dummy with whatever you've got!"

Frisk sighed, reluctantly backing out of the ACT option and selecting FIGHT instead. "What do I even hit with?!" they asked hurriedly.

"ANYTHING!"

Frisk looked around, then spotted a stick laying on the ground just next to them. They reached down to grab it, and held it firmly in their hand. Then, they jerked around and hit the raging dummy with it, using all of their might.

The stick seemed to go right through the dummy.

 _MISS._

"What?!" Frisk and Flowey said at once.

The dummy took great amusement to this, and laughed. "FOOLS! I am a ghost! I cannot be hurt by any such physical attack!"

Frisk's eyes widened and they began to slowly shake with terror. "Um, d-don't panic!" Flowey cried, trying to reassure the poor child. "The dummy said that it can't get hit by _physical_ attacks, right? So what if I used a _magic_ attack?! See, Frisk? We'll be oka—"

But Flowey hadn't even realized that while he was talking, Frisk had instead opened the ACT menu. They selected the option 'Talk.'

 _You talk to the dummy_.

 _It doesn't seem much for conversation._

 _No one is happy with this._

"FOOL! Fight me or die!" the dummy cried with anger.

Flowey wished that he could facepalm. "Frisk, what are you doing?! I told you, you have to learn how to FIGHT if you want to survive down here! But for now, get behind me and I'll—"

But Frisk wasn't listening anymore. Determined to solve this problem without fighting the dummy, they opened the ACT menu again, this time selecting the option 'Compliment.'

 _You compliment the dummy._

 _It calms down a little._

"Ngh…complimenting?! S-such tactics will not work on me!" the dummy denied, flustered.

Both Frisk and Flowey gasped at this response. It was obvious that complimenting was doing something. Frisk selected the same option again.

 _You compliment the dummy some more._

 _It seems happier._

"Nobody has ever said such nice things to me," the dummy sniffled. Its little stitched mouth was curved into a smile, and it floated back down to the ground. The dark background around the trio disappeared, and was replaced by the previous surroundings. Frisk's eyes widened into a hopeful gaze as they watched their red soul disappear in front of them. Had they done it…?

"Thank you, human, for showing me kindness," the dummy said. "It's just that…no one ever shows kindness in the Underground. Not even a little. Everyone down here is full of hate and despair; monsters only have one goal, and that is to take our rightful surface back from those dirty humans. However…we cannot get to the surface until the barrier keeping us trapped down here is broken. And in order to break it, our king, Asgore Dreemurr, needs to collect seven human souls."

"H-human souls…?" Frisk squeaked. They were suddenly tense.

The dummy huffed, avoiding the small child's gaze. "Yes. And so far, he has gathered six. All he needs is one more…listen, human, you're in danger. Monsters were banished underground for a reason—most will kill any human in sight. It isn't safe here. Escaping is going to be difficult, but not impossible. But seeing how determined you were in that battle, I believe that you can do it."

Frisk sniffled. "You think so?"

The dummy nodded. "Now, you better get going. Toriel might be having her daily stroll through the Ruins right now."

"Who's…Toriel?" Frisk asked nervously.

"I'll tell you on the way," Flowey answered this time. "Come on, Frisk. Let's get going."

After a seemingly-cheerful goodbye to the dummy, Frisk and Flowey continued their journey. It was pretty quiet, and neither of them spoke a word until they were walking down a long hallway that seemed to go on for miles. After Flowey reassured Frisk by telling them that the hallway was not, in fact, infinite, he decided to explain.

"So…Toriel." Flowey took a deep breath. It was hard to think of her as anything but his mother. But…that wasn't true anymore. As much as he hated to admit it, he was no longer Asriel. He had broken away from his former self so long ago. So he tried not to think about that minor fact as he explained to Frisk, "Toriel is a monster who often patrols the Ruins, searching for humans who have potentially fallen down such as yourself. She…well…uh, how do I say this? She—"

"She seems nice," Frisk noted.

Flowey gave a dry laugh. "She's anything _but_ nice. At first glance, she may seem like a kind, loving woman, and I'll be honest with you, I fell for her act many times." He bent his head in shame. "Once you get close to her, you'll discover what she's really like…there was a certain human who once fell into the Ruins long ago. They met Toriel, and like any other unsuspecting person, gave her their trust. Unfortunately, their life was cut short when Toriel wondered what a human would taste like and…she ate them."

Frisk stopped walking and turned their head to look at Flowey whom was resting on their arm with unease. "Did you just say that she ate them?"

Flowey sighed. "You heard me right. You know that monster I was describing a bit earlier, who won't hesitate to eat you? Yeah, I was talking about her. Monsters in the Underground fear her, often telling each other rumors on how family members have disappeared, most likely kidnapped by Toriel and baked in one of her pies or something. Weird, I know, but I tend not to question it."

Frisk rubbed their neck. "So…how are we going to get out of the Ruins if we have to deal with her?"

"Hopefully we don't encounter her," Flowey said, "but it's likely that we will; there's an easy way out of the Ruins, but it's through her house, so unless she's gone and left the place unlocked, then..."

Frisk was silent.

"Hey, I know this sounds pretty bad, Frisk," Flowey murmured, "but this is the cruel reality of the Underground. It's going to be scary and intimidating, but if you want to get home, then you'll have to face it. ACTing won't always work…in some situations, you'll have to fight, and even kill. Remember, in this world, it's kill or be killed. And hey, don't look so down. At least you've got me to keep you from dying, right?"

Frisk looked at Flowey. He winked at them, which made them giggle, a small smile appearing on their lips. "Okay…thanks, Flowey."

"No problem," Flowey replied. The two were now a lot more contented than before. "Now, I don't know about you, but I'm ready to get out of here," the flower chuckled. Frisk nodded firmly, and started to walk down the hallway once more.

Yes, Frisk was only a child, and they had to admit they were scared of what was to come. But what Flowey said had cheered them up. Hopefully, with enough determination, they could conquer anything. There was a skip in their step as they pictured themself back at their home, nestled warmly in their bed, crickets chirping outside their window under a moonlit sky.


End file.
